The present invention relates to a data processing system and method which are arranged to keep loads at data processing nodes well-balanced as much as possible.
As a method of accessing data in a database system composed of plural nodes, conventionally, two methods, that is, a shared database approach and a shared nothing database approach are disclosed in Sohan DeMel, “Oracle9i Real Application Clusters—Cache Fusion Delivers Scalability,” Oracle White Paper, Oracle Corporation, pages 7 to 9 and 12 to 13, May 2001.
The shared database approach method is arranged to allow each of the nodes to evenly make access to all data. Hence, this method makes it possible to uniformly distribute load among the nodes. This method, however, requires synchronous update among the nodes, which brings about overheads such as an I/O process of reading data again and an inter-node communication for synchronous control.
On the other hand, the shared nothing database approach method permits each of the nodes to make access to only a data area allocated to each node itself. Hence, if the data location is shifted, the load is focused on one or some nodes. However, this method does not require the synchronous control among the nodes, so that the nodes may be operated in parallel.